Report dropped spans in client reports

[cleptric]

Description

SDKs that emit client reports today should record an additional dropped span category event when a transaction is dropped, containing the number of the spans inside the transaction plus one.
The plus one stems from the fact that Relay extracts an additional span from the transaction. If a transaction contains no spans, we still want to report one dropped transaction and one dropped span. This also applies to transactions that are not sampled.
If certain spans are dropped in beforeSendTransaction, an event processor etc., we also want to report those if feasible.

{
	"discarded_events": [
		{
			"reason": "something",
			"category": "transaction",
			"quantity": 1
		},
		{
			"reason": "something",
			"category": "span",
			"quantity": 3 // 2 spans + 1 span (the transaction itself should be counted)
		}
	]
}

See https://www.notion.so/sentry/Rate-Limited-Outcomes-for-Nested-Spans-in-Transactions-1ba24e34bdb64e9498aa5c03ecb28ba0?d=eeb2093683d541f5996e6eb804713236#3c019a03b165493d989440bc67c8c5be for more details.

---

SDKs which emit standalone spans today, should additionally implement handling span category rate limits, which only apply to standalone spans.

Why should we be doing this?

We need to to be able to report over quota and other rejection stats for AM3 customers. As we currently do not emit this data, the billing page shows spans as zero.

Why now?

We didn’t understand the full extend of the reporting of outcomes before hand, hence this came up post AM3 launch.

Stakeholder(s)

@phacops @cleptric

Team(s)

All SDK teams

SDKs

Beta Give feedback

1. Docs: Document span client reports sentry-docs#11283
2. Report dropped spans in client reports sentry-javascript#12727
   +0
   
3. Report dropped spans in client reports sentry-python#3229
   +0
   
4. PHP SDK -> no client reports yet
5. Laravel SDK -> no client reports yet
6. Symfony SDK -> no client reports yet
7. Go SDK -> no client reports yet
8. Report dropped spans in client reports sentry-ruby#2341
   enhancement +1
   
9. Elixir SDK -> no client reports yet
10. Report dropped spans in client reports sentry-java#3527
    Platform: Android Platform: Java +2
    
11. Report dropped spans in client reports sentry-dotnet#3458
    +0
    
12. Unity SDK -> inherits from .NET
13. PowerShell SDK -> inherits from .NET
14. Unreal SDK -> inherits from .NET/Native
15. Android SDK (via Java SDK)
16. Report dropped spans in client reports sentry-cocoa#4156
    Platform: Cocoa +1
    
17. Cordova SDK (via Javascript SDK)
18. Report dropped spans in client reports sentry-dart#2137
    3 of 3
    Platform: Dart +1
    
19. Flutter SDK (via Dart SDK)
20. Kotlin Multiplatform SDK
21. Report dropped spans in client reports sentry-react-native#3944
    3 of 3
    Platform: React-Native +1
22. Native SDK -> no client reports yet
23. Report dropped spans in client reports sentry-capacitor#693
    3 of 3
    Platform: Capacitor Status: Backlog +2
24. Rust SDK

[krystofwoldrich]

@cleptric Recording of dropped spans is currently implemented in JS v8, which means RN SDK will have it in the next major version, when updated to v8. Is that okay, or should we backport the recording to JS v7?

[kahest]

@cleptric on sentry-native we don't have client reports yet (updated tasklist accordingly) - lmk if we need to implement client reports from scratch for this

[cleptric]

@krystofwoldrich when will the next RN major ship?

@kahest No, we agreed on only doing this for SDKs already supporting client reports. I still think each SDK should have them one day, but no need to do this right now.

[kahest]

@cleptric the next RN major is scheduled for early September, so in about a month

[krystofwoldrich]

I opened getsentry/sentry-javascript#13343 to port this to v7. So RN and Capacitor can just bump the JS version.